gistfile1.rb

def daemonize(name = File.basename($0), options = {})
  pid_path = options[:pid_path] || File.expand_path("tmp/pids/#{name}.pid")

  # If the pid file exists, check that the process is actually still running.
  begin
    if File.exists?(pid_path) && Process.kill(0, File.read(pid_path).to_i)
      $stderr.puts "Already running."
      exit 1
    end
  rescue Errno::ESRCH
    File.delete(pid_path)
  end

  at_exit do
    File.delete(pid_path)
    logger.error("#{$!.class}: #{$!.message}\n#{$!.backtrace.join("\n")}") if $!
  end

  Process.daemon(true)

  # Open with File::::EXCL, File::CREAT, and perms to avoid race conditions
  # (i.e. a malicious symlink in a shared dir)
  File.open(pid_path, File::RDWR|File::EXCL|File::CREAT, 0600) { |io| io.write(Process.pid) }
end

not likely it'll race between the lines, but still nice I think.